Metal Roofing: tips and tricks to avoid specification and installation failure.

The secret is in the fix
August 8, 2019

Metal Roofing: tips and tricks to avoid specification and installation failure.

What are the installation techniques for varying metal roofing fastening systems?

The roof is one of your most important architectural elements of your project as it serves as protection against natural elements. Because of this it is important to take into consideration the roof type, pitch, aesthetics and type of material when planning your project. Sheet metal roofing has gained popularity amongst architects as it is economic, durable and versatile and enhances the aesthetics of a project. Sheet metal roofing can be used for any type of residential, industrial or commercial building and depending on the material the roof slopes can be as little as 1°, however National Building regulations advises a 5° pitch. Depending on the climatic conditions, supporting structures and design influencing roof design, the installation and the type of fastening system used for your metal roof is a deciding factor to consider in the early design & planning phases or your metal roof

There are two main types of installation techniques/fastening systems to consider on your project, which is either a Pierced fixed roofing technique (Positive fix) or a Concealed fixed (Non-positive fix) roofing technique.

Pierced fixed type roofs are typically used in conventional roof types and is mainly used for roofing profiles such as Inverted Box Rib (IBR), Corrugated and Widespan roofing profiles. A Fastener (nails/screws) is used to fix/positive fix the sheet metal to the purlin/lipped channel/timber truss by penetrating through the metal sheeting. Perforations are then unavoidable in the crest of the sheeting. With pierced fixed roofing, the roof is fixed directly onto the purlin/truss which then limits thermal expansion on the roof and due to this it may cause that the fastening points wear out and can create leakage over time.

Example of IBR roof sheeting profile:

Concealed fixed type roofs are generally used for commercial and industrial projects such as warehouses, factories, schools and shopping centers. For Concealed fixing/non-positive fixing methods there is no perforation of the sheeting and no fasteners penetrate through the sheeting (such as Craft-Lock®/Reehfalz concealed fixing systems). For a concealed fix system such as Craft-Lock®, the profile is formed with a female & male lip  on the longitudinal edges of the sheet, the male lip is fastened by means of a cleat onto the purlin and the female rib is then seated over the male rib in a sideways interlocking manner. The female rib conceals the fixing cleat and this system then allows freedom of movement for thermal expansion and contraction and eliminates stress on the fastening systems.

Example of Craft-Lock® concealed roofing system:

Long life fasteners are a key component of a properly installed roof, why?

The lifespan of your roof is dependent on the type of fastener used for your roof. What seems as such a small cost element of your roof can in the long run cost you much more when the wrong type of fastener is used. In consideration when choosing a fastener, it is important to note the type of fastener and compatibility of the type of metal material and coatings used with the fastener. It is often overlooked that fasteners need to resist climate, material compatibility and loading conditions. A roof can be done with the best roofing system and material, but if the fasteners fail early, it defeats the purpose.

Refer to more information on the SAISC article at

How do you choose metal roofing types?

Depending on the project requirement, each roof type needs to be fit for purpose. If you need a more flexible roof design with natural curves and that withstand heavy wind loads- metal roofing is then the product of choice. Metal roofing is versatile, lightweight and more economic than any other roofing material and is up to 80% lighter than using heavier roofing types for example concrete tiles. Because of the light-weight feature of steel, it in turn saves on the roof structure, construction time and the cost of the project. As steel is readily formable, metal roofing offers the designer a variety of colours, material finishes (gloss, matt & textured), the freedom of design and creativity which makes it suitable for a wide variety of roof design features.

How do specify a concealed fixed roof for your project?

There are 5 factors to consider when specifying metal roofs for your project:

  1. Material thickness– this is the thickness of the material used to manufacture the roof sheets (0.58mm, 0.5mm, 0.53mm, 0.8mm)
  2. Material type– This refers to the type of material. There are 2 main categories – Painted (Chromadek®, Colorbond®, ColorPlus®) and unpainted (ZincAL®, Galvanised, Zincalume®, Copper, Mill finish Aluminium etc)
  3. Coating thickness – This refers to the protective coating thickness of the steel substrate, like Z200, Z275, AZ100, AZ150 etc, where a Z200 grade will mean 200 grams of zinc per square meter or AZ150 will mean 150 grams of Aluzinc per square meter.
  4. Yield Strength– This refers to the material grade (ISQ300, G275, G300)
  5. Profile– Type of profile- Pierced fixed (Widespan, Corrugated & IBR) or concealed fixed (Craft-Lock®, Rheefalz)

Herewith below a typical Craft-Lock® Concealed fix roof sheeting specification for a project:

Craft-Lock® Concealed fix roof sheeting with a male/female sideways interlocking mechanism, forming a double capillary action break manufactured from

(1)0.58mm thick (2)ISQ 300 steel with (3)Chromadek® finish, colour (Fish Eagle White) 

with a (4) Z 275  (5) Galvanized coating.

(1)      Refers to your thickness of choice

(2)      Refers to the correct material grade

(3)      Refers to the desired finish

(4)      Refers to the desired protective coating mass

(5)      Refers to the desired protective coating  

Why is specification on your steel roof an important factor to consider?

Profile type, material thickness, coating types, yield strengths and paint finishes can often be a confusing combination to get right when it comes to specifying the type of roof to be used on a project. It is therefore critically important to specify each aspect correctly. Ambiguity in specification leads to either honest mistakes or willful manipulation by contractors or subcontractors on projects, where lower quality products end up on projects than were intended by architects or developers. By taking the time to write a clear specification and omitting wording such as “similar or approved” will lead to clients and professionals having roofs on their projects that they chose initially.

What are important factors to consider in steel roof design?

  • Soft roof vs Hard roof
    • A metal roof is considered a soft roof. Although roof traffic on the roof is possible due to the strength of the roof, it is often abused by following trades such as HVAC or further wet work trades. A sensible site program as well as roof design that places HVAC and other services on hard roofs or where designated walkways are installed in high traffic maintenance areas, will improve the quality if the roof and its performance over time.
  • Site conditions
    • Consider the method of getting roof sheets on the roof in a manner that will not cause scratches or dents, which could lead to aesthetically or mechanical damage.
  • Construction program
    • Allowing following trades or wet works to use a steel roof as a platform to work from, will cause significant damage and problems to the professional team and clients. A program that allows for the completion of all wet works around and above roofs will mitigate this risk so that metal roof sheeting can be installed in an environment that will lead to a quality finished product.
  • Location of services
    • Placing services in areas that have dedicated access that don’t require traffic on the steel roof is ideal. This is not always possible and in such cases, the installation of walkways is highly recommended to protect the integrity of the roof over time.

 Example of roof damage on roofs that can affect your warranty/cause installation failure:

  • Services that penetrate the roof, without proper flashing and sealing
  • Grinding swarf that is not cleaned from roofs after they are deposited on the roof.
  • Heavy roof traffic in areas like cat ladders, services or construction areas in vicinity or on top of roof.
  • Following or other trades using the roof as an area to mix cement, place scaffolding, place brick pallets etc, cause massive damage to roofs that were previously in perfect condition.

What best practices would you recommend for steel metal roofing?

  • It is recommended that there are no construction or maintenance traffic on roofs
  • Services on “hard roofs” are recommended with internal access
    • If traffic is unavoidable:
      • Install temporary walkways with marine ply
      • Design permanent walkways with compatible clips and steel walkways onto the roofs
    • Choose the correct profile type, considering the roof design.
    • Ensure penetrations through roofs are dealt with in accordance to best practices
    • Ensure the correct grade and type of fixings are used
    • Don’t push construction programs to such an extent that roofs are used as construction platforms as this can lead to the complete destruction and replacement of roofs, defeating the purpose of the cost savings of a faster program
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